The present invention relates generally to the field of optical communications systems. More specifically, the present invention discloses an optical interferometer for demultiplexing an optical signal.
Wavelength division multiplexing is a commonly used technique that allows the transport of multiple optical signals, each at a slightly different wavelength, over an optical fiber. The ability to carry multiple signals on a single fiber allows that fiber to carry a tremendous amount of traffic, including data, voice, and digital video signals. For example, the International Telecommunications Union (ITU) Draft Recommendation G.mcs proposes a frequency grid which specifies various channel spacings including 100 GHz and 200 GHz.
Interferometers can be used as wavelength routers to multiplex or demultiplex optical signals for WDM communications. When performing the multiplexing function, an interferometer combines two input WDM signals, each containing sets of optical channels, into a single, more densely spaced output signal. When used as a demultiplexer, an interferometer separates an input WDM signal containing a plurality of optical channels at different wavelengths into two, more widely spaced sets of channels. In particular, interferometers can be employed to divide the spectral space evenly with alternating optical channels being directed to each output port (i.e., odd wavelength channels 1, 3, 5, 7, etc. are directed to a first output port, while even wavelength channels 2, 4, 6, etc. are directed to a second output port). This function has sometimes been called an optical interleaver. This function is inherently bi-directional and can also be used to multiplex two sets of input channels (containing the even and odd channels, respectively) into a single output signal.
One of the difficulties in making a practical interferometer is the stabilization of the optical path length in the device, which affects the wavelength stability of the device. Materials in the interferometer can change index of refraction and physical dimension when subjected to temperature and mechanical perturbations. In the past, others have resorted to temperature control of the optical cavity, compensation of material index change by making composites of dissimilar materials, and birefringent interferometers. In contrast, the present invention discloses an optical interferometer architecture that is stable, compact, and requires no temperature control.
One embodiment of the present invention is an apparatus for processing an optical signal that includes a tunable optical element and a reflective element. The tunable optical element receives an input signal at an incidence angle and separates the input signal into a first beam having a first optical path length and a second beam having a second optical path length. The difference between the first optical path length and the second optical path length is based at least in part upon the incidence angle of the input signal. The reflective element reflects the first beam and the second beam such that the first beam interferes with the second beam to produce a first output signal and a second output signal. The first output signal comprises a first subset of wavelength channels from the input signal and the second output signal comprises a second subset of wavelength channels from the input signal.
Another embodiment of the present invention is a method for processing an optical signal that includes receiving an input signal at an incidence angle. The method proceeds by separating the input signal into a first beam having a first optical path length and a second beam having a second optical path length. The difference between the first optical path length and the second optical path length is based at least in part upon the incidence angle of the input signal. The method concludes by interfering the first beam with the second beam to produce a first output signal and a second output signal. The first output signal comprises a first subset of wavelength channels from the input signal and the second output signal comprises a second subset of wavelength channels from the input signal.
Yet another embodiment of the present invention is an optical system that includes a demultiplexer network, an optical component coupled to the demultiplexer network, and a multiplexer network coupled to the optical component. The demultiplexer network demultiplexes an input WDM signal into a plurality of wavelength channels and includes a tunable optical element and a reflective element. The optical component processes a portion of the wavelength channels. The multiplexer network multiplexes a portion of the wavelength channels to generate an output WDM signal.
The following technical advantages may be achieved by some, none, or all of the embodiments of the present invention. An interferometer of the present invention provides an optical element that may be dynamically tuned to control the optical path lengths of the beams used in the operation of the interferometer. In this regard, the wavelength channel spacings of the resulting signals may be dynamically controlled whether the interferometer is used as a demultiplexer or a multiplexer. In this respect, the interferometer comprises a bi-directional device that allows for tunability, stability, and robust operation in a compact architecture.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.